From Julia Witt, SH (ASCP), Hematology Supervisor, Smith-Glynn-Callaway Clinic, Springfield, MO:
Monday, December 26: We recently had a patient present with an MI. He is on a standard treatment regiment. Upon his arrival at the hospital, baseline coagulation studies were performed. The fibrinogen result exceeds the linearity of the analyzer. A 1:1 dilution utilizing pooled normal plasma yielded a normal fibrinogen result of 130. Clearly this patient has some type of interference, but what could it be?
Follow-up on Wednesday, December 28 from Julia: This is how it turned out. Our hospital laboratory uses the Stago Evolution for their fibrinogen testing. When running this patient, the Stago was giving a VMAX error, implying a > linearity limit result. The patient was receiving Activase to resolve a clot and the physician was concerned (needless to say) because the Activase should have been depleting this patient’s fibrinogen, not raising it. It turns out the clot time is inversely proportional to the actual result, so if the instrument gives a VMAX error, it means the patient result is below linearity. All is fixed now, but what a great educational opportunity and a reminder of how important it is to know your coagulation analyzer!
Thank you for this anecdote, Julia. Without your clarification I was prepared to suggest the odd fibrinogen results could be related to treatment. The direct thrombin inhibitors argatroban, lepirudin, bivalirudin, and dabigatran can generate discrepant fibrinogen values in which the Clauss assay, which is thrombin time-based, generates results much lower than the turbidometric estimate from optical coagulometers. This turns out not to be the case for your patient.
As you conclude, this is a good opportunity to mention that the Clauss assay generates an inverse proportional relationship, meaning the longer the clot time, the lower the fibrinogen level. That’s why the Evolution reports a VMAX indication when the fibrinogen is low.